Flight Recorders - Flight Data Recorders (FDRs)
Flight Data recorders record at least the last 25 hours of flight information. Tape
based units employ either an endless multitrack tape, or a reel to reel multitrack
tape. The flight data is recorded digitally in a serial data stream on the tape.
The number of flight parameters recorded is dependant upon the vintage and size
of the aircraft. The most basic system record as few as 5 parameters, the most complex
records thousands of parameters.
Some FDR contain the digital to analogue converters (ARINC 542), other recorders
accept data from a FDAU (ARINC 573, 717, 747).
Tape Units
The flight data is converted to digital data and then recorded onto tape serially.
The tape is organized into tracks. New data is recorded over the oldest data, preserving
at least 25 hours of flight data.
Only the tape mechanism is protected in the crash and fire protected module.
Solid State Units
The flight data is stored in non-volatile memory.
The solid state recorders record the parameters that change during a flight. If
the aircraft is in cruise flight many parameters are stable and not changing, memory
is conserved, thus solid state recorders store much more than 25 hours of flight
data.
Solid state recorders are much lighter than tape based recorders. The latest generation
are sometimes as much as 40% lighter.
Flight Data Readouts
Here in Canada, the Canadian Air Regulations require that a Correlation check be
done every 3000 hours or 12 months which ever occurs first to ensure all required
parameters are being recorded and usable. This is usually done by a readout of the
last flight recorded by the FDR. The readout allows the Maintenance crew to confirm
that the data is valid and representative of the last flight. Depending on the number
of parameters recorded, and the duration of the flight the report can be many hundreds
of pages long.